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Erik Smolders

Publications and source records attributed to Erik Smolders.

15 recordsLinked to original sources
PubMed2006

Terrestrial biotic ligand model. 2. Application to Ni and Cu toxicities to plants, invertebrates, and microbes in soil.

The Terrestrial Biotic Ligand Model (TBLM) is applied to a number of noncalcareous soils of the European Union for Cu and Ni toxicities using organisms and endpoints representing three levels of terrestrial organisms: higher plants, invertebrates, and microbes. A comparison of the TBLM predictions to soil metal concentration or free metal ion activity in the soil solution shows that the TBLM is able to achieve a better normalization of the wide variation in toxicological endpoints among soils of disparate properties considered in this study. The TBLM predictions of the EC50s were generally within a factor of 2 of the observed values. To our knowledge, this is the first study that incorporates Cu and Ni toxicities to multiple endpoints associated with higher plants, invertebrates, and microbes for up to eleven noncalcareous soils of disparate properties, into a single theoretical framework. The results of this study clearly demonstrate that the TBLM can provide a general framework for modeling metals ecotoxicity in soils.

Animals↗
PubMed2006

Labile Cd complexes increase Cd availability to plants.

Dissolved trace metals are present in the environment as free ions and as complexes. Commonly used models to predict metal bioavailability consider the free ion as the major bioavailable species. However, increases in metal availability in the presence of metal complexes have repeatedly been found. We measured the uptake of cadmium (Cd) by spinach (Spinacia oleracea) from solution in absence or presence of synthetic ligands. At the same free ion concentration, the uptake of Cd ranged over almost 3 orders of magnitude and was largest in treatments with fast dissociating (i.e. labile) complexes. Similar results were found for the diffusional fluxes in these solutions, as measured with the DGT technique. The observed effect of Cd complexes on the plant uptake was in agreement with model calculations in which plant uptake was assumed to be governed by the diffusional flux. These results strongly suggest that Cd uptake is rate-limited by diffusion of the free ion to the root surface, even in stirred solutions. As a result, dissolved Cd complexes can increase Cd uptake, resulting in apparent exceptions from the free ion activity model. The magnitude of this increase depends both on the concentration and on the lability of the complexes. The free ion concept should therefore be reconsidered when transport limitations of the metal ion to the uptake site prevail.

Biological Availability↗
PubMed2006

Long-term exposure to elevated zinc concentrations induced structural changes and zinc tolerance of the nitrifying community in soil.

A series of long-term Zn-contaminated soils was sampled around a galvanized pylon. The potential nitrification rate (PNR) was unaffected by the soil total Zn concentrations up to 25 mmol Zn kg(-1) whereas spiking the uncontaminated control soil with ZnCl(2) to identical total concentrations completely eliminated nitrification. The larger sensitivity of the PNR to spiked ZnCl(2) than to the Zn added in the field was equally found when relating the PNR to the Zn concentrations in the pore water of these soils, suggesting differences in Zn tolerance of the nitrifying communities. Zinc tolerance in the long-term Zn-contaminated soil was demonstrated by showing that (i) the nitrifying community of long-term Zn-contaminated soil samples was less sensitive to Zn than that of the uncontaminated control soil when both communities were inoculated in sterile ZnCl(2)-contaminated soil samples, and, that (ii) addition of ZnCl(2) to the long-term Zn-contaminated soil samples affected nitrification less than equal additions of ZnCl(2) to uncontaminated control samples. Denaturing gradient gel electrophoresis fingerprinting of polymerase chain reaction amplified 16SrRNA gene fragments of ammonia-oxidizing bacteria showed that the community structure in uncontaminated and long-term contaminated soil samples was different and could be related to soil Zn concentrations.

Adaptation, Physiological↗
PubMed2006

Soil properties affecting the toxicity of CuC12 and NiC12 for soil microbial processes in freshly spiked soils.

It generally is unknown to what extent the toxicity of Cu and Ni for soil microbial processes varies among different soils. A comparative study was made using three different microbial assays (nitrification potential, glucose-induced respiration, and C-mineralization of a plant residue) in 19 (for Cu) or 16 (for Ni) soils with contrasting soil properties. Each soil was spiked with CuCl2 or NiCl2 at seven different concentrations, and the bioassays were started after a 7-d equilibration period. The Cu and Ni toxicity thresholds varied 19- to 90-fold among soils. The differences in both Cu and Ni toxicity among soils were neither explained by soil solution metal concentrations nor by free ion activities calculated from soil solution composition. Copper toxicity thresholds (total concentrations) increased with increasing organic matter content or cation exchange capacity (CEC) and, surprisingly, decreased with increasing pH depending on the assay. Nickel toxicity thresholds consistently increased with increasing CEC, background Ni, and clay content for all three assays. Thresholds expressed as soil solution free ion activities all significantly decreased with increasing soil solution pH (r2 = 0.57-0.93), consistent with a decreased H+:M2+ competition at the biological membrane. That competition largely counteracts the H+:M2+ competition for sorption, effectively explaining the insignificant or weak effect of pH on total Ni or Cu toxicity thresholds. It is concluded that free metal-ion activity alone does not explain variation in metal toxicity among soils.

Biodiversity↗
PubMed2006

Discrepancy of the microbial response to elevated copper between freshly spiked and long-term contaminated soils.

A systematic comparison of Cu toxicity thresholds was made between freshly spiked soils and soils in which elevated Cu concentrations have been present for various times. Three uncontaminated soils were spiked and experimentally leached or incubated outdoors for up to 18 months. Additionally, five field-contaminated soils with a 6- to 80-year-old Cu contamination were sampled, and corresponding uncontaminated soils were spiked to identical total concentrations. All soil samples were subjected to three microbial assays (nitrification potential, glucose-induced respiration, and maize residue C-mineralization). Experimental leaching or soil incubation after spiking reduced Cu toxicity (1.3- or 2.3-fold increase of dose, respectively, to inhibit process by 50% [ED50]). No significant effects of soil type, aging time (6, 12, or 18 months), or bioassay on the factor change of ED50 were found. Significant reductions of microbial activity in field-contaminated soils were only identified in 2 of the 15 series (three assays in five soils), whereas freshly spiking the corresponding control soils significantly affected these processes in 12 series. Soil solution Cu concentrations significantly decreased on leaching at corresponding total soil Cu, and smaller decreases were found during additional aging. Soil solution Cu concentrations largely explain changes in Cu toxicity on leaching and aging, although additional variation may be related to changes in the sensitivity of microbial populations. It is concluded that total Cu toxicity thresholds are lower in freshly spiked soils compared to soils in which Cu salts have equilibrated and leaching has removed excess soluble salts. The large variability of soil microbial processes creates a large uncertainty about the magnitude of the factor by which aging mitigates Cu toxicity.

Aging↗
PubMed2006

Model studies of corrosion-induced copper runoff fate in soil.

Laboratory experiments have been performed with 3-cm soil columns simulating the fate of corrosion-induced copper runoff in contact with soil. The investigation simulates approximately 30 years (assuming an infiltration surplus of 25 cm/year) of continuous percolation of copper containing runoff water of a concentration realistic at the immediate release situation (4.8 mg/L) into four soils representative of urban conditions. Two of the three investigated topsoils reached their breakthrough of copper within the simulated time, while the third topsoil did not show a breakthrough. The subsoil reached a breakthrough after approximately 10 years of simulated exposure. To simulate more realistic outdoor scenarios, the laboratory-obtained breakthrough curves were modeled with Hydrus-1D using a Langmuir-Freundlich model to describe copper sorption, the parameters of which were estimated from soil properties (pH, organic carbon content). The model predicts longer breakthrough times with increasing pH and organic content of the soil and with decreasing concentrations of copper and dissolved organic carbon in the runoff water. The time span for copper in runoff water (at concentrations of 0.01-10 mg/L) to reach a soil depth of 50 cm varied between 170 and more than 8,000 years for the predicted field scenarios.

Agriculture↗
PubMed2006

Effect of leaching and aging on the bioavailability of lead to the springtail Folsomia candida.

Because it is unclear if leaching can account for differences in metal bioavailability observed between metal-spiked soils and historically contaminated field soils, we simultaneously assessed Pb toxicity to the springtail Folsomia candida in three transects of Pb-contaminated soils and in leached and unleached soils spiked at similar total Pb concentrations. Total Pb concentrations of 3,877 mg/kg dry weight and higher always caused significant effects on F. candida reproduction in the spiked soils. In the transects, only the soil with the highest Pb concentration of 14,436 mg/kg dry weight significantly affected reproduction. When expressed as pore-water concentrations, reproduction was never significantly affected at Pb concentrations of 0.539 mg/L, whereas reproduction was always significantly affected at Pb concentrations of 0.678 mg/L and higher, independent of the soil treatment. These results indicate that pore-water Pb concentrations can explain, at least in part, the observed differences in the toxicity data expressed as total Pb concentrations. Leaching after the spiking procedure only caused small differences in Pb toxicity and, therefore, cannot account for toxicity differences between laboratory-spiked soils and historically contaminated field soils.

Biological Availability↗
PubMed2005

Modelling 137Cs uptake in plants from undisturbed soil monoliths.

A model predicting 137Cs uptake in plants was applied on data from artificially contaminated lysimeters. The lysimeter data involve three different crops (beans, ryegrass and lettuce) grown on five different soils between 3 and 5 years after contamination and where soil solution composition was monitored. The mechanistic model predicts plant uptake of 137Cs from soil solution composition. Predicted K concentrations in the rhizosphere were up to 50-fold below that in the bulk soil solution whereas corresponding 137Cs concentration gradients were always less pronounced. Predictions of crop 137Cs content based on rhizosphere soil solution compositions were generally closer to observations than those based on bulk soil solution composition. The model explained 17% (beans) to 91% (lettuce) of the variation in 137Cs activity concentrations in the plants. The model failed to predict the 137Cs activity concentration in ryegrass where uptake of the 5-year-old 137Cs from 3 soils was about 40-fold larger than predicted. The model generally underpredicted crop 137Cs concentrations at soil solution K concentration below about 1.0 mM. It is concluded that 137Cs uptake can be predicted from the soil solution composition at adequate K nutrition but that significant uncertainties remain when soil solution K is below 1 mM.

Cesium Radioisotopes↗
PubMed2005

Toxicity of heavy metals in soil assessed with various soil microbial and plant growth assays: a comparative study.

Abstract-Elevated metal concentrations in soils can disturb the soil ecosystem; thus, researchers strive to identify the most sensitive assay for detection of the early signs of toxicity. The purpose of the present study was to compare eight different ecotoxicological endpoints on the same set of metal-contaminated soils that were collected from seven series of soils sampled during field trials. The endpoints are based on three microbial assays (potential nitrification rate [PNR], substrate-induced respiration [SIR], and basal respiration [BR]) and two plant growth tests, one of which included symbiotic N fixation. The overall sensitivity of the endpoints to detect statistically significant adverse effects ranked as follows: PNR > SIR (lag time) > plant yield and N fixation > SIR (respiration after 24 and 48 h) > BR. The lowest adverse effect concentrations were found with the PNR at 7 mg kg(-1) of Cd and 107 mg kg(-1) of Zn. The variability of these endpoints among different uncontaminated soils was additionally assessed on 14 soil samples. That variability showed a strong correlation with sensitivity scores, illustrating that metal-sensitive endpoints have a large natural variability. We question the ecological relevance of highly sensitive microbial assays, because they tend to have a large natural variability. The identification of toxicity in the field requires endpoints that are highly sensitive and that do not vary greatly among soils (i.e., robust); however, no such endpoint was found in the present study. The endpoints that combined average sensitivity and robustness were SIR (lag time), clover yield, and N fixation in clover.

Cadmium↗
PubMed2004

Kinetics of Zn release in soils and prediction of Zn concentration in plants using diffusive gradients in thin films.

Effective concentrations (CE) of Zn measured by the technique of DGT (diffusive gradients in thin films) were compared, along with total concentrations of Zn and the concentrations of Zn in soil solutions, to Zn concentrations in plants. Soils variously contaminated with Zn were collected in the vicinity of two galvanized electrical transmission towers (pylons) and two motorway crash barriers. Lepidium sativum was grown in each soil and in corresponding control soils amended with ZnCl2 to similar total Zn concentrations. CE, concentrations in soil solution, and total Zn were measured in all soils, and total Zn was measured in the plant shoots. The CE values, soil solution Zn, and shoot Zn concentrations were all larger in ZnCl2 amended soils than in field contaminated soils at corresponding total Zn. Correlations between the concentration of Zn in the plants and the measured soil parameter followed the order CE > soil solution > total Zn. The low scatter in the plot of log plant concentration versus log CE revealed a relationship with two distinct features. Plant Zn was between 100 and 300 mg/kg up to an effective Zn concentration of about 2 mg/L, above which plant Zn increased steadily with increasing CE. Use of a dynamic model to interpret the DGT measurement suggests that the intrinsic rate of release of Zn from solid phase to solution, expressed as a rate constant, is much higher for soils that receive fresh supplies of Zn. This finding provides a mechanistic basis for reconciling laboratory experiments, where metal is freshly amended, to data obtained in the field. The potential of DGT as a surrogate for metal availability to plants is further confirmed by this work.

Belgium↗
PubMed2004

Soil properties affecting toxicity of zinc to soil microbial properties in laboratory-spiked and field-contaminated soils.

The effects of soil properties and zinc (Zn) availability on the toxicity of Zn to soil microbial processes are poorly understood. Three soil microbial processes--potential nitrification rate (PNR), substrate (glucose)-induced respiration (SIR), and a maize residue respiration (MRR)--were measured in 15 European topsoils (pH 3.0-7.5; total Zn 7-191 mg/kg) that were freshly spiked with ZnCl2. The Zn toxicity thresholds of 20 to 50% effective concentrations (EC20s and EC50s) based on total concentrations of Zn in soil varied between 5- and 26-fold among soils, depending on the assay. The Zn toxicity thresholds based on Zn concentrations in soil solution varied at least 10-fold more than corresponding total metal thresholds. Soil pH had no significant effect on soil total Zn toxicity thresholds, whereas significant positive correlations were found between these thresholds and background Zn for the PNR and SIR test (r = 0.74 and 0.71, respectively; log-log correlations). No such trend was found for the MRR test. Soil solution-based thresholds showed highly significant negative correlations with soil pH for all assays that might be explained by competition of H+ for binding sites, as demonstrated for aquatic species. The microbial assays were also applied to soils collected under galvanized pylons (three sites) where concentrations of total Zn were up to 2,100 to 3,700 mg Zn/kg. Correlations between concentrations of total Zn and microbial responses were insignificant at all sites even though spiking reference samples to equivalent concentrations reduced microbial activities up to more than 10-fold. Differences in response between spiked and field soils are partly but not completely attributed to the large differences in concentrations of Zn in soil solution. We conclude that soil pH has no significant effect on Zn toxicity to soil microbial processes in laboratory-spiked soils, and we suggest that community tolerance takes place at both background and elevated Zn concentrations in soil.

Biological Availability↗
PubMed2003

Relating soil solution Zn concentration to diffusive gradients in thin films measurements in contaminated soils.

The technique of diffusive gradients in thin films (DGT) has been suggested to sample an available fraction of metals in soil. The objectives of this study were to compare DGT measurements with commonly measured fractions of Zn in soil, viz, the soil solution concentration and the total Zn concentration. The DGT technique was used to measure fluxes and interfacial concentrations of Zn in three series of field-contaminated soils collected in transects toward galvanized electricity pylons and in 15 soils amended with ZnCl2 at six rates. The ratio of DGT-measured concentration to pore water concentration of Zn, R, varied between 0.02 and 1.52 (mean 0.29). This ratio decreased with decreasing distribution coefficient, Kd, of Zn in the soil, which is in agreement with the predictions of the DGT-induced fluxes in soils (DIFS) model. The R values predicted with the DIFS model were generally larger than the observed values in the ZnCl2-amended soils at the higher Zn rates. A modification of the DIFS model indicated that saturation of the resin gel was approached in these soils, despite the short deployment times used (2 h). The saturation of the resin with Zn did not occur in the control soils (no Zn salt added) or the field-contaminated soils. Pore water concentration of Zn in these soils was predicted from the DGT-measured concentration and the total Zn content. Predicted values and observations were generally in good agreement. The pore water concentration was more than 5 times underpredicted for the most acid soil (pH = 3) and for six other soils, for which the underprediction was attributed to the presence of colloidal Zn in the soil solution.

Colloids↗
PubMed2003

Comparison of toxicity of zinc for soil microbial processes between laboratory-contamined and polluted field soils.

Soil microbial processes are readily disturbed by added zinc (Zn) in laboratory ecotoxicity tests. This study compares Zn toxicity between freshly spiked soils and soils that have been contaminated with Zn in the field. Soils were sampled in three transects (< 80 m) toward galvanized electricity transmission towers (pylons). The soil total Zn concentrations gradually increased in each transect from background values (25-82 mg Zn/kg) to elevated Zn concentrations near the pylon (226-595 mg Zn/kg). Soil samples taken at the furthest distance from the Zn source were spiked with ZnCl2 to a range of total Zn concentrations similar to those in the transect. Nitrification, respiration, and N-mineralization rates were significantly reduced by added Zn in laboratory-spiked soils and were 9 to 95% (mean 32%) of the control values at largest doses depending on soil type and the microbial process. In contrast, these processes were either unaffected by soil Zn (p > 0.05) or increased significantly with soil Zn concentrations in the transect soils. These increases could not be explained by soil pH or % soil organic carbon. Leaching soils after spiking significantly lowered the toxic effects of Zn on nitrification or on substrate-induced respiration. The soil solution Zn concentrations of field soils were always smaller than in spiked soils at equivalent total Zn. Highest soil solution Zn concentrations were always lower than the soil-solution EC50s of spiked soils. It is concluded that there is a large discrepancy in microbial responses to elevated Zn between spiked soils (unleached) and field-contaminated soils and there is a need to explain this discrepancy in terms of Zn availability, adaptation processes, and additional soil factors controlling the microbial processes.

Laboratories↗
PubMed2002

Fate and effect of zinc from tire debris in soil.

Tire debris contains significant quantities of zinc (Zn), and there is concern about the diffuse Zn contamination of soils from tire wear. An experiment was set up to quantify the fate and effect of Zn from tire debris in soil. Two different soils were mixed with the <100-microm fraction of car and truck tire debris (25 g kg(-1) soil) or zinc sulfate (ZnSO4) as a reference. Soils were transferred to soil columns with free drainage and placed outdoors for 11 months. Leachates of the tire debris amended soils did not contain significantly (P>0.05) more Zn than control soils except for a 3-fold increase in one soil amended with cartire debris. The increase in Zn leaching due to tire debris was only 3% of the corresponding increase in the ZnSO4 treatment at the same total Zn in soil. Tire debris application increased the soil nitrification potential, whereas ZnSO4 application, at corresponding or smaller total Zn concentration, decreased nitrification potential. An increase in soil pH was observed in all soils treated with tire debris and explains the increased nitrification potential. About 10-40% of the Zn from tire debris was isotopically exchangeable in soil sampled after 1 year weathering. It is concluded that a significant fraction of Zn is released from the rubber matrix within 1 year, but the parallel increase in soil pH limits the mobilization of Zn in soil.

Belgium↗